Automated Billing?

I'm looking for opinions/suggestions on how to handle billing of clients. What do those of you have have many clients do to handle billing and payments? Did you build a custom module, or are you using a 3rd party tool?

Thanks Till. It's good to know an integrated solution will be possible. I'll have to look at the tracker and svn to see how far along it is. In the meantime, my question still is: what do people currently use to handling billing?

Thanks Till. It's good to know an integrated solution will be possible. I'll have to look at the tracker and svn to see how far along it is. In the meantime, my question still is: what do people currently use to handling billing?